Abstract: In this paper, the digital image based triaxial shear test, computed tomography (CT) scanning test and scanning electron microscopy (SEM) test were employed to investigate triaxial shear behavior and microstructure evolution of basalt fiber reinforced loess subjected to drying?wetting cycles. The results show that the shear failure mode of soil samples with relatively higher basalt fiber content changes from overall bulging failure to shear band failure with the increase in the number of drying?wetting cycles, while the shear failure mode exhibits an opposite trend with the increase in the fiber content at the early stage of drying?wetting process. Neither drying?wetting cycle nor fiber content has obvious effect on the type and characteristics of stress?strain curves, and both of them present strain-hardening behavior. The deviatoric stress at failure decreases with the increasing number of drying?wetting cycles; however, the attenuation rate gradually decreases. The deviatoric stress at failure first increases and then decreases with the increasing fiber content, showing a parabolic variation, and the optimal fiber content is 0.6%. A similar trend is observed between the ME value of CT scanning and the deviatoric stress at failure. Drying?wetting action induces cracking and loosening around the soil-fiber interface, thus weakening the fiber reinforcement effect. However, compared with unreinforced loess, fiber reinforced loess demonstrates strong overall stability in its microstructure. The macroscopic and microscopic damage variables reflecting the drying?wetting induced deterioration of loess samples were finally established, which shows a consistent variation trend.

Key words: drying?wetting cycles, basalt fiber reinforced loess, digital image technology, triaxial shear test, damage variable